The present disclosure relates to a developing device configured to supply a developer to an image carrier and an image forming apparatus including the developing device.
In the electrographic image forming apparatus, an electrostatic latent image formed on the surface of an image carrier (a photosensitive drum) is developed as a toner image in the developing device, and the developed toner image is transferred from the image carrier to a sheet in a transferring unit. A developer which is dispersed in the vicinity of the developing device or the transferring unit or a developer remaining on the image carrier after transferring of the toner image is often recovered, replenished into the developing device and reused.
A technique in which the recovered developer is replenished into the developing device and reused has been in a wide spread. However, the recovered developer has a low amount of charge, is charged in a reverse polarity or often has a small particle diameter. Therefore, there is a tendency that an image failure such as a fogging due to a poor charge in reuse occurs. In addition, when the recovered developer is mixed with a developer supplied from the toner container, a replenishment fogging due to a difference of a charging amount also is generated. Such an image failure is accelerated by aged deterioration of the developer, a decrease of the charging amount due to environmental change or the like.
With respect to the problems, there is a developing device configured to reproduce a developer by applying an external additive into the recovered developer.